1. Field of the Invention
The invention relates to a disk brake with a self-energized brake effect particularly for brake systems for vehicles and other technical devices.
2. Background Discussion
In disk brakes normally used, particularly in vehicles, the braking force is generated between the rotating brake disk and the brake shoe accommodated in the caliper by means of hydraulic, electric or pneumatic means, the pressure of which acts on at least one piston installed in the side wall of the stationary caliper. Due to the resulting piston movement the brake shoe directly or indirectly connected to it is pressed against the brake disk rotating with the axletree with its friction lining in parallel to the axle. In the so called floating caliper disk brakes two brake shoes or brake pads are simultaneously pressed against the plane-parallel faces of the respective brake disk. To achieve the required high braking forces the hydraulic piston/cylinder units and their main cylinders need to have relatively large dimensions, which requires mounting space and requires, accordingly, large operating forces on the brake pedal. Different systems of power brakes operated with servo power effect an automatic increase in the pressing forces of the brake shoes with comparably lower pedal operating forces and enable the usage of smaller hydraulic assemblies. Such power brake systems, however, are technically complex and expensive.
Although various disk brakes with an integrated power brake have become known, they have, however, generally not been introduced in practice and particularly in vehicle manufacturing since they obviously do not fully met the complex requirements in year-long driving service.
In German patent 1,284,731 a partially lined disk brake is described, the caliper of which is borne on a tappet fixed to the vehicle with an elongated pole so as to be axially movable. The piston of the hydraulic cylinder mounted in a caliper pole is provided with a pivotable pressure part which engages with a carrier plate of the one brake shoe and allows certain movements of the pressed-on brake shoe in the circumferential direction of the brake disk. The pivotable and axially movable carrier plate of hardened steel has a saw-tooth shaped corrugated profile, the elevations and valleys of the corrugation extending in the radial direction. A steel member fixed to the caliper pole has a corrugated profile adjusted thereto and is in positive engagement with the carrier plate. When the hydraulic cylinder is operated, the pivotally borne carrier plate is moved in the circumferential direction by a small amount due to the frictional engagement of the brake lining and the brake disk. The corrugations, which are thereby displaced with respect to each other, will cause a wedge effect and thus an increased contact pressure of the brake shoes, that is, an increased brake effect. An intended influence on this power brake effect is impossible and problems may arise, particularly in long-term service, due to caking and contamination of the two corrugations. Further, considerable manufacturing requirements must be fulfilled for such disk brakes.
For obtaining a self-energizing effect in a disk brake, German patent 1,019,873 proposes the provision of brake shoe guides contained in the caliper poles under an angle of more or less than 90xc2x0 with respect to the plane-parallel brake disk faces and bearing the respective brake shoes in the guide of the caliper by means of rolling bodies. The amount of the self-energizing effect changes on its own by the pivotable formation of a pivoting shoe guide.
According to German patent publication 2,837,634 self-energizing of a disk brake may also be obtained by integrating a snap ring extending in the circumferential direction into the brake disk, the edges of the snap ring being inclined in certain angles with respect to the disk surface. Into the snap ring an accordingly wedge-shaped shoulder of the respective brake shoe is pressed, a force acting radially inward being generated by the interaction of the two inclined surfaces.
In Japanese patent abstracts 2-102933 and 56-6931 disk brakes are described, the brace disks of which are cone-shaped with the wall width increasing radially outwardly. The brake shoes, which are hydraulically movable in conventional calipers, can only carry out axial movements in the direction of the axis of the brake disk, and the shape of the brake linings is adjusted to the cone shaped profile of the brake disk. These brake disks have no self-energized braking action.
It is a primary purpose of the invention to provide a disk brake having a self-energized braking effect which has a particularly simple construction compared to known embodiments and by which an operationally safe and efficient self-energizing effect is obtained even in long-term use.
Since in the subject matter of the invention the distance between the bearing arrangement of the brake shoes and the brake disk axis is larger than the distance between the center of gravity of the application of force of the respective brake shoe and the brake disk axis, that is, the bearing arrangement is disposed radially outside of the centers of gravity of the application of force, the brake shoes are taken along by the rotating brake disk within the amount of their free movability and simultaneously moved about the pivot axis of the bearing arrangement by a predetermined value due to the frictional engagement of their brake linings. This movement leads to a radial displacement of the center of gravity of the application of force of the brake shoes to the outside with respect to the brake disk. Since the faces of the brace disk interacting with the brake linings on the brake shoes have a predetermined inclination with respect to the axis of the brake disk, the motion of the brake disk results in an increased contact pressure of the brake linings, which means a correspondingly increased braking effect.
The disk brake according to the invention is particularly suited for an assembly into vehicles with one or more tracks since its constructive requirements and its dimensions are approximately equal to those of conventional vehicle disk brakes and therefore no problems concerning positioning in the vehicles will arise and the assembly may also be effected in the common way. The disk brake according to the invention may particularly efficaciously be used as a so called locking brake or overunning brake in different types of trailers since the self-energizing effect occurs even with the slightest rotational movements of the wheels and their brake disks and even with only a small contact pressure of the brake linings in the beginning and will increase progressively.
The self-energizing effect obtainable according to the invention may be selected so that the pressure forces acting only axially on the brake shoes may be drastically decreased as compared to conventional disk brakes. Thus, there arises the possibility to omit the hydraulic power generators so far regarded as absolutely necessary in vehicle manufacturing and to replace them by simpler and cheaper mechanical or electromagnetic actuating systems. Besides, the dimensions of the different devices may be decreased or the hydraulic pressures lowered, or both, while maintaining the hydraulic power generators, which in both cases will have advantageous effects on the manufacturing costs and the safety of operation. Since the actuation forces required for generating the brake effect are relatively small compared to the corresponding actuation forces of conventional brake systems, fluid transmission means, that is, hydraulics or pneumatics, including all related additional devices, may be omitted. Instead, electric actuator motors or solenoids acting directly or indirectly on the brake shoes may be provided on the brake calipers for power generation. With such a use of electric actuation and transmission means in vehicle combinations (towing vehicle and trailer) for which overrunning brake systems are mandatory, so called xe2x80x9ccontinuousxe2x80x9d brake systems as are mandatory in larger vehicle combinations may be designed with the realization of the disk brake according to the invention.
In the disk brake according to the invention the two brake shoes disposed laterally adjacent to the brake disk are borne in a xe2x80x9cfloatingxe2x80x9d manner and can be moved in the tangential direction with respect to the brake disk within predetermined limits. Those movements are effected by a clinging of the brake shoe to the rotating brake disk during the start of the braking operation, the amount of the movement being limited by the interaction of a stopper bolt of the respective brake shoe in a stopper bore of larger diameter.
Compared to known embodiments the disk brake of the invention has the particular advantage that high braking forces or brake effects are obtained by means of relatively small actuating forces even over longer operating times. Since the increased brake forces preferably act in the rotational direction of the disk, the pressure forces oriented parallel to the axis and generated by the hydraulic or pneumatic components may be reduced which enables a lighter construction of the brake calipers. Another advantage resides in the use of the disk brakes according to the invention in combination with common mechanical overrunning means of trailers, whereby a good adjustment of the overall braking reaction of towing vehicle and trailer is obtained since both may be provided with disk brakes. While in conventional brake systems for towing vehicles and trailers different media were required for controlling and operating the individual devices, which rendered a considerable technical complexity necessary, the use of the disk brake principle according to the invention in complex vehicle systems, such as towing vehicles with trailers attached to them, makes it possible to omit various devices and components, which results in a reduction of manufacturing costs while maintaining at least the same safety of operation. Furthermore, for the first time so called continuous brake systems become feasible even for simple vehicle combinations which previously could only be provided with non-continuous overrunning brake systems.
For commercial vehicle combinations so called continuous brake systems, in which the control and operation of the brakes are transferred to the trailer through the towing vehicle by means of conduits, and the brakes of the trailer work in synchronism with the brakes of the towing vehicle, are prescribed by law. In lighter combinations of towing vehicle and trailer without such continuous brake systems the trailers are provided with so called overrunning brakes. During the operation of the brakes of the towing vehicle the trailer, which is not braked in the beginning, will apply a thrust force to the towing vehicle through its draw-bar. That thrust force is used to generate the actuating forces for the wheel brakes of the trailer in the above overrunning brake systems. When such a towing vehicle/trailer combination is to drive backward from a standstill, the driver previously had to get out of the towing vehicle to activate a mechanical lock on the draw-bar of the trailer to prevent an actuation of the trailer""s brakes by the thrust forces applied to the trailer by the towing vehicle during reverse travel.
Modem vehicles or vehicle combinations are required to be provided with so called reverse gear automatics which will automatically release the wheel brakes of the trailer during reverse travel. At the start of the reverse movement of the towing vehicle the draw-bar of the trailer is pushed together by prescribed amounts, which causes a limited advance movement of the brake shoes in the direction of the brake surfaces, for example, via mechanical lever rod assemblies, without generating any other perceptible brake effect (compare German patent publication 196 09 629).
According to an important aspect of the invention reverse gear automatics are realized in a technically simple way by supporting the brake shoes with only one bearing arrangement on the rear side with respect to the normal turning direction so that they are freely movable in a limited way. When an inversion of the turning direction of the wheel and with it of the brake disk occurs with this hinging of the movable brake shoe, the respective brake shoe is moved radially inward in the direction toward the rotational axis of the brake disk due to the effect of the wedge surfaces. Since the wall thickness of the brake disk continually decreases toward the radially inner side, a correspondingly larger clearance is created for the brake shoes. Since the advance path of the brake shoes generated by the hydraulic actuation cylinders is always limited, a position in which the brake linings are free from the active surfaces of the brake disk, and therefore no braking effect is present any longer, is reached due to the radial movement of the brake shoes to the inside. Thus, a trailer provided with the disk brake of the invention suspended on one side enables an automatic release of the trailer brakes during reverse travel. When the vehicle combination runs forward again, the normal positioning of the brake linings is self-restored during the following braking operation, and upon operation of the brake pedal the brake system of the towing vehicle and of the trailer works with the self-energized power brake in the way described above.